U.S. patent application number 12/862679 was filed with the patent office on 2010-12-23 for burner for manufacturing porous glass base material.
This patent application is currently assigned to SHIN-ETSU CHEMICAL CO., LTD.. Invention is credited to Makoto YOSHIDA.
Application Number | 20100323311 12/862679 |
Document ID | / |
Family ID | 41015799 |
Filed Date | 2010-12-23 |
United States Patent
Application |
20100323311 |
Kind Code |
A1 |
YOSHIDA; Makoto |
December 23, 2010 |
BURNER FOR MANUFACTURING POROUS GLASS BASE MATERIAL
Abstract
The present invention provides a burner for manufacturing a
porous glass base material that has small-diameter gas discharge
ports and that achieves uniform linear velocity at the gas
discharge ports, a uniform reaction, and a stable flame, and
improved deposition efficiency. In the burner for manufacturing a
porous glass base material, inner diameters of the pipes forming
the gas discharge ports positioned farther inward in a radial
direction than the gas discharge ports in which the small-diameter
gas discharge port nozzles are arranged contract beginning from a
position farther on a burner source side than the prescribed length
L position, the contraction being greater closer to a burner tip
side, and inner diameters of the pipes forming the gas discharge
port in which the small-diameter gas discharge port nozzles are
arranged and the gas discharge ports that are positioned farther
outward in the radial direction than this gas discharge port
contract beginning from a position farther on a burner tip side
than the prescribed length L position, the contraction being
greater closer to a burner tip side.
Inventors: |
YOSHIDA; Makoto; (Ibaraki,
JP) |
Correspondence
Address: |
Masao Yoshimura
333 W. El Camino Real, Suite 380
Sunnyvale
CA
94087
US
|
Assignee: |
SHIN-ETSU CHEMICAL CO.,
LTD.
Tokyo
JP
|
Family ID: |
41015799 |
Appl. No.: |
12/862679 |
Filed: |
August 24, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2009/000884 |
Feb 27, 2009 |
|
|
|
12862679 |
|
|
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|
Current U.S.
Class: |
431/187 |
Current CPC
Class: |
C03B 2207/14 20130101;
C03B 2207/06 20130101; C03B 2207/12 20130101; C03B 19/1423
20130101; C03B 2207/42 20130101; C03B 37/0142 20130101; Y02P 40/57
20151101 |
Class at
Publication: |
431/187 |
International
Class: |
F23D 14/22 20060101
F23D014/22 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2008 |
JP |
2008-046833 |
Feb 17, 2009 |
JP |
2009-034224 |
Feb 25, 2009 |
JP |
2009-042296 |
Claims
1. A burner for manufacturing porous glass base material,
comprising: a central pipe that is arranged centrally and has a
central raw material gas discharge port formed therein; a plurality
of pipes that are coaxial with the central pipe and that form
annular gas discharge ports between adjacent pipes; and a plurality
of small-diameter gas discharge port nozzles that (i) are arranged
in one or more rows in a circle coaxial with the central pipe
within one of the gas discharge ports other than the central raw
material gas discharge port, (ii) have small-diameter gas discharge
ports formed therein, and (iii) branch from one main pipe arranged
between a pair of pipes forming the gas discharge port in which the
nozzles are arranged, at a position that is a prescribed length L
from tips of the nozzles, wherein inner diameters of the pipes
forming the gas discharge ports positioned farther inward in a
radial direction than the gas discharge ports in which the
small-diameter gas discharge port nozzles are arranged contract
beginning from a position farther on a burner source side than the
prescribed length L position, the contraction being greater closer
to a burner tip side, and inner diameters of the pipes forming the
gas discharge port in which the small-diameter gas discharge port
nozzles are arranged and the gas discharge ports that are
positioned farther outward in the radial direction than this gas
discharge port contract beginning from a position farther on a
burner tip side than the prescribed length L position, the
contraction being greater closer to a burner tip side.
2. The burner for manufacturing porous glass base material
according to claim 1, wherein in the small-diameter gas discharge
port nozzles, small-diameter gas discharge ports in the same row
have identical focal distances.
3. The burner for manufacturing porous glass base material
according to claim 1, wherein (i) the inner diameters of the pipes
forming the gas discharge ports positioned farther inward in the
radial direction than the gas discharge port in which the
small-diameter gas discharge port nozzles are arranged and (ii) the
inner diameters of the pipes forming the gas discharge port in
which the small-diameter gas discharge port nozzles are arranged
and the gas discharge ports that are positioned farther outward in
the radial direction than this gas discharge port contract from the
burner source side toward the burner tip side with a prescribed
contraction ratio X, such that X.ltoreq.0.83.
4. The burner for manufacturing porous glass base material
according to claim 1, wherein with an aperture diameter of the
outer pipe forming the gas discharge port in which the
small-diameter gas discharge port nozzles are arranged being
represented as D, a relationship between the prescribed length L
and the aperture diameter D fulfills an expression
L/D.gtoreq.2.0.
5. The burner for manufacturing porous glass base material
according to claim 1, wherein at least the pipes forming the gas
discharge ports positioned farther inward in the radial direction
than the gas discharge port in which the small-diameter gas
discharge port nozzles are arranged are formed to be thinner closer
to the burner tip side, in the portions where the inner diameters
contract.
6. The burner for manufacturing porous glass base material
according to claim 1, wherein a burner cover is disposed on an
outer side of the outermost pipe of the burner, and is formed to
maintain a prescribed clearance relative to the outermost pipe of
the burner.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a burner for manufacturing
a porous glass material having good deposition efficiency.
[0003] The contents of the following Japanese patent applications
are incorporated herein by reference,
[0004] No. 2008-046833 filed on Feb. 27, 2008,
[0005] No. 2009-034224 filed on Feb. 17, 2009,
[0006] No. 2009-042296 filed on Feb. 25, 2009, and
[0007] PCT/JP2009/000884 filed on Feb. 27, 2009
[0008] 2. Related Art
[0009] Various conventional methods have been proposed for
manufacturing an optical fiber base material. One such method is
OVD (Outside Vapor Phase Deposition), which involves relatively
moving the burner or a starting member back and forth to affix and
deposit glass fine particles generated in the burner flame onto the
rotating starting member to synthesize the porous base material,
and dehydrating and sintering this base material in an electric
furnace. With this method, an optical fiber base material having a
relatively arbitrary refractive index distribution can be obtained
and mass production of optical fiber base materials with large
aperture diameters can be achieved, and so this method is commonly
used.
[0010] FIG. 1 is a schematic view showing an exemplary porous glass
base material manufacturing apparatus that uses the OVD method. In
FIG. 1, the starting member on which the glass fine particles
(soot) are deposited is realized by dummy rods 2 fused at both ends
of a core rod 1, and the ends of the dummy rods 2 are supported by
ingot chuck mechanisms 4 to be rotatable on an axis. The optical
fiber raw material, vapor such as SiCl.sub.4, and a combustion gas
such as hydrogen gas and oxygen gas are blown toward the starting
member from the burner 3 that moves back and forth relative to the
starting member, and the optical fiber porous base material is
formed by depositing on the starting member the soot generated by
the hydrolysis in the oxygen flame. Here, reference numeral 5
indicates an exhaust hood.
[0011] The burner 3 is supported to move back and forth in the
longitudinal direction of the starting member via a burner guide
mechanism, not shown. While the starting member rotates on an axis,
the burner blows the flame toward the starting member, thereby
forming the porous base material by depositing glass fine particles
generated by the hydrolysis of the raw material gas in the flame.
Next, the porous base material is passed through a heater of a
heating furnace, not shown, to become dehydrated glass, thereby
forming the optical fiber base material.
[0012] In order to synthesize the glass fine particles and deposit
the soot on the starting member, a burner having a plurality of
coaxial pipes is conventionally used. However, such a burner is
unable to generate a sufficient amount of glass fine particles,
since there is insufficient mixing of the glass raw material gas,
the combustion gas, and the auxiliary combustion gas. As a result,
the yield cannot be increased and the high-speed synthesis becomes
difficult.
[0013] In order to solve this problem, Japanese Examined Patent
Application Publication No. 03-9047 proposes a multi-nozzle burner
having a plurality of nozzles within the combustible gas discharge
port that form small aperture diameter auxiliary combustion gas
discharge ports arranged to surround the central raw material gas
discharge port. With this type of burner, several methods for
improving deposition efficiency are proposed. For example, Japanese
Patent Application Publication No. 2003-206154, Japanese Patent
Application Publication No. 2004-331440, Japanese Patent
Application Publication No. 2006-182624, and Japanese Patent No.
3744350 propose small aperture diameter auxiliary combustion gas
discharge ports. Furthermore, Japanese Patent Application
Publication No. 05-323130, Japanese Patent No. 3543537, and
Japanese Patent Application Publication No. 2003-226544 describe
optimization of the focal distances of the small aperture diameter
auxiliary combustion gas discharge ports. Japanese Patent No.
3591330, Japanese Patent Application Publication No. 2003-165737,
Japanese Patent Application Publication No. 2003-212555, and
Japanese Patent No. 3653902 describe optimizing the gas flow rate
and gas linear velocity.
[0014] The inventors of the present invention performed a rigorous
investigation of a burner for manufacturing a porous glass base
material having small-diameter auxiliary combustion gas discharge
ports, i.e. nozzles. As a result, it was found that the deposition
efficiency is strongly linked to the configuration and focal
distances of the small-diameter auxiliary combustion gas discharge
ports, the gas flow rate, and the gas linear velocity. However,
there have been problems such as a non-uniform reaction caused by a
variation of the gas linear velocity in the gas discharge ports and
disruption of the flame caused by unstable gas flow, and these
problems interfere with improvements to the deposition
efficiency.
[0015] Usually, the supply of a reaction gas to the burner involves
disposing gas inlet pipes at certain locations near the source side
of the pipes forming the gas discharge ports, and supplying the
reaction gas to each gas discharge port via supply tubes connected
to the gas inlet pipes. The gas supplied to the gas discharge ports
is supplied from gas inlet pipes connected at certain locations in
a direction orthogonal to a ring-shaped (annular) flow path, but is
not supplied to the central gas discharge port. Here, since the
burner is configured as multiple coaxial pipes, pipes farther
outward have larger diameters, and the gas supplied from the gas
inlet pipes to the ring-shaped flow path has difficulty flowing
around on an opposite side of the inner pipes when these pipes are
positioned farther outward. As a result, it is easy for the linear
velocity in a flow path cross section of the gas discharge ports to
become non-uniform.
[0016] In particular, a burner having small-diameter auxiliary
combustion gas discharge ports has a group of the small-diameter
auxiliary combustion gas discharge ports arranged within one gas
discharge port, and so compared to a conventional burner with
coaxial pipes that does not have small-diameter auxiliary
combustion gas discharge ports, a variation of the linear velocity
of the gas from the gas discharge ports is more likely to occur.
Therefore, a method is considered for reducing linear velocity
variation within the gas discharge ports by disposing a plurality
of gas inlet pipes in the pipes forming the gas discharge ports,
but this is difficult to realize because a large number of gas
inlet pipes are necessary, resulting in a very complex
configuration.
[0017] It is an object of the present invention to provide a burner
for manufacturing porous glass base material that has
small-diameter gas discharge ports and that can achieve uniform
linear velocity, a uniform reaction, a stable flame, and improved
deposition efficiency.
SUMMARY
[0018] Therefore, it is an object of an aspect of the innovations
herein to provide a burner for manufacturing porous glass base
material, which is capable of overcoming the above drawbacks
accompanying the related art. The above and other objects can be
achieved by combinations described in the independent claims. The
dependent claims define further advantageous and exemplary
combinations of the innovations herein.
[0019] According to a first aspect related to the innovations
herein, one exemplary burner may include a burner for manufacturing
porous glass base material, comprising a central pipe that is
arranged centrally and has a central raw material gas discharge
port formed therein; a plurality of pipes that are coaxial with the
central pipe and that form annular gas discharge ports between
adjacent pipes; and a plurality of small-diameter gas discharge
port nozzles that (i) are arranged in one or more rows in a circle
coaxial with the central pipe within one of the gas discharge ports
other than the central raw material gas discharge port, (ii) have
small-diameter gas discharge ports formed therein, and (iii) branch
from one main pipe arranged between a pair of pipes forming the gas
discharge port in which the nozzles are arranged, at a position
that is a prescribed length L from tips of the nozzles, wherein
inner diameters of the pipes forming the gas discharge ports
positioned farther inward in a radial direction than the gas
discharge ports in which the small-diameter gas discharge port
nozzles are arranged contract beginning from a position farther on
a burner source side than the prescribed length L position, the
contraction being greater closer to a burner tip side, and inner
diameters of the pipes forming the gas discharge port in which the
small-diameter gas discharge port nozzles are arranged and the gas
discharge ports that are positioned farther outward in the radial
direction than this gas discharge port contract beginning from a
position farther on a burner tip side than the prescribed length L
position, the contraction being greater closer to a burner tip
side.
[0020] The summary clause does not necessarily describe all
necessary features of the embodiments of the present invention. The
present invention may also be a sub-combination of the features
described above. The above and other features and advantages of the
present invention will become more apparent from the following
description of the embodiments taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic view showing an apparatus for
manufacturing a porous glass base material using OVD.
[0022] FIG. 2 is a schematic view showing the tip of a conventional
burner for synthesizing glass fine particles having small-diameter
gas discharge ports.
[0023] FIG. 3 is a schematic cross-sectional view showing a
conventional burner having small-diameter gas discharge ports.
[0024] FIG. 4 is a schematic view describing measurement positions
for linear velocity variation of gas at the burner tip, with the
position of the gas inlet pipe as a reference.
[0025] FIG. 5 is a schematic view describing measurement positions
for linear velocity variation of the gas discharge port containing
the small-diameter gas discharge ports.
[0026] FIG. 6 shows the linear velocity variation of a conventional
burner having the small-diameter gas discharge ports.
[0027] FIG. 7 is a schematic cross-sectional view showing an
embodiment of the burner having the small-diameter gas discharge
ports according to the present invention, which is used in the
First Embodiment.
[0028] FIG. 8 shows linear velocity variation of the burner used in
the First Embodiment.
[0029] FIG. 9 is a schematic view showing the state of gas flow in
the third pipe of the burner used in the First Embodiment.
[0030] FIG. 10 shows the relationship between the contraction ratio
X (B/A) of the inner diameters of the pipes and the deposition
efficiency.
[0031] FIG. 11 is a schematic view showing the state of the gas
flow in the third pipe when the L/D ratio is low.
[0032] FIG. 12 shows the linear velocity variation of the burner
when the L/D ratio is low.
[0033] FIG. 13 shows the relationship between the L/D ratio and the
deposition efficiency.
[0034] FIG. 14 is a schematic view showing the appearance of the
burner when the burner cover is disposed outside the outermost
pipe.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0035] Hereinafter, some embodiments of the present invention will
be described. The embodiments do not limit the invention according
to the claims, and all the combinations of the features described
in the embodiments are not necessarily essential to means provided
by aspects of the invention.
[0036] The following is a detailed description of an embodiment of
a burner for manufacturing porous glass base material according to
the present invention, and references FIG. 7.
[0037] The burner 100 of the present embodiment is configured with
coaxial overlapping pipes that include a first pipe 101 having a
raw material gas discharge port 101P formed in the center thereof,
and around which is formed a plurality (second through fifth) of
pipes 102, 103, 104, 105 which form a plurality (second through
fifth) of coaxial annular gas discharge ports 102P, 103P, 104P, and
105P. The first through fifth pipes 102, 103, 104, and 105 have
cross-sectional surfaces in the axial direction that are
circular.
[0038] In the present embodiment, a first gas inlet pipe 109.sub.1
is disposed to be coaxial with the central first pipe 101 which
forms the raw material gas discharge port 101 P (referred to
hereinafter as the "first gas discharge port") centered on the axis
C. The second pipe 102, the third pipe 103, the fourth pipe 104,
and the fifth pipe 105 are sequentially arranged to be coaxial with
the first pipe 101, and the second gas inlet pipe 109.sub.2, the
third gas inlet pipe 109.sub.3, the fourth gas inlet pipe
109.sub.4, and the fifth gas inlet pipe 109.sub.5 are disposed on
the source side of the burner 100 in directions orthogonal to the
central axis C.
[0039] One main pipe 108 is arranged between the second pipe 102
and the third pipe 103, starting from the source side and extending
to a position that is a prescribed length L from the tip of the
burner 100. The main pipe 108 is closed at the position that is
length L from the tip of the burner by a barrier 108A that is
continuous with an inner periphery of the second pipe 102. A sixth
gas inlet pipe 109.sub.6 is disposed at the source-side of the main
pipe 108 in a direction orthogonal to the central axis C. Nozzles
106N, in which are formed a plurality of small-diameter gas
discharge ports 106P at the position of the prescribed length L,
branch from the barrier 108A of the main pipe 108. In the present
embodiment, the small-diameter gas discharge port nozzles 106N are
contained within the third gas discharge port 103P formed between
the second pipe 102 and the third pipe 103, and are arranged at
uniform intervals in a line around the central axis C of the first
pipe 101 in which the raw material gas discharge port 101P is
formed. In the present embodiment, there are eight nozzles. Each
small-diameter gas discharge port nozzle 106N is bent inward in the
radial direction in a manner to have the same focal distance on the
central axis C. The small-diameter gas discharge port nozzles 106N
may be arranged at uniform intervals in two lines on coaxial
circles around the central axis C.
[0040] The first gas discharge port 101P and the second gas
discharge port 102P, which are positioned farther outward in the
radial direction than the third gas discharge port 103P that
contains the small-diameter gas discharge port nozzles 106N, are
formed such that, from a position at a length Lx that is farther
toward the burner source side than the position that is length L
from the tip, the inner diameter of the pipe in which the ports are
formed begins to decrease, such that the inner diameter of the pipe
is constant on the tip side of the length L position. In other
words, the first pipe 101 and the second pipe 102, which are
positioned farther inward than the third gas discharge port 103P
containing the small-diameter gas discharge port nozzles 106N, have
diameters that continuously decrease from the length Lx position to
the length L position. When the inner diameters of the pipes on the
burner 100 source side where the gas inlet pipes 109.sub.1 and
109.sub.2 are disposed are each represented as A and the inner
diameter of these pipes on the burner 100 tip side are each
represented as B, the pipes having the first and second gas
discharge ports are formed to contract, such that the contraction
ratio X of the inner diameters thereof each satisfy the expression
X=B/A.ltoreq.0.83.
[0041] On the other hand, the third gas discharge port 103P
containing the small-diameter gas discharge port nozzles 106N and
the fourth gas discharge port 104P and fifth gas discharge port
105P positioned outward in the radial direction from the third gas
discharge port 103P have inner diameters that contract beginning
from a length Ly position that is farther toward the burner tip
side than the position that is length L from the tip. In other
words, the third through fifth pipes 103 to 105 that are positioned
outward from the small-diameter gas discharge port nozzles 106N
have diameters that continuously decrease from the length Ly
position to the burner 100 tip. When the inner diameters of the
pipes from the length L position to the length Ly position are each
represented as A and the inner diameter of these pipes at the
burner 100 tip are each represented as B, the pipes having the
third to fifth gas discharge ports 103P to 105P are formed to
contract, such that the contraction ratio X of the inner diameters
thereof each satisfy the expression X=B/A.ltoreq.0.83.
[0042] When the third pipe 103, in which the third gas discharge
port 103P is formed having the small-diameter gas discharge port
nozzles 106N arranged therein, has an aperture diameter D, the
third pipe 103 is formed such that the relationship between the
aperture diameter D and the prescribed length L fulfils the
condition L/D.gtoreq.2.0. By having a sufficient length L for the
small-diameter gas discharge port nozzles 106N, uniform linear
velocity can be achieved for the gas flow around the small-diameter
gas discharge port nozzles 106N.
[0043] In the present embodiment, the first and second pipes 101
and 102, which form the first and second gas discharge ports 101P
and 102P positioned farther outward in the radial direction than
the third gas discharge port 103P in which the small-diameter gas
discharge port nozzles 106N are arranged, have contracted portions
where the inner diameters thereof are contracted beginning at the
length Lx position and ending at the length L position. In these
contracted portions, the thickness of the pipes gradually decreases
farther toward the burner 100 tip, and this decreased pipe
thickness is maintained from the length L position to the burner
100 tip. Furthermore, the fifth pipe 105 which forms the fifth gas
discharge port 105P has a contracted portion where the inner
diameter thereof decreases from the length Ly position to the
burner 100 tip, and in this contracted portion the pipe thickness
decreases towards the burner 100 tip. This enables a more compact
shape for the overall burner 100.
[0044] As shown in FIG. 14, a burner cover 110 is disposed on the
outside of the fifth pipe 105, which is the outermost pipe of the
burner 100, and is formed to have a constant clearance with respect
to the fifth pipe 105. By providing this burner cover 110, the
overall burner 100 can be made more compact.
[0045] The following describes an embodiment of the present
invention and a comparative example, but the present invention is
not limited to this embodiment.
EMBODIMENTS
Preliminary Investigation
[0046] First, in the preliminary investigation, variation of linear
velocity at the tip of a conventional burner, such as shown
schematically in FIGS. 2 and 3, was measured for each gas discharge
port.
[0047] This burner has a coaxial pipe structure, wherein eight
small-diameter gas discharge port nozzles 16 are contained in a
third pipe 13 and these small-diameter gas discharge port nozzles
16 are arranged at uniform intervals in a circle centered on a
central pipe 11. As shown in FIG. 3, a small-diameter gas discharge
port nozzle 16 is formed to branch from the burner main pipe 18 at
a position, shown by the reference numeral 17, that is L=80 mm from
the burner tip.
[0048] A gas for manufacturing porous glass base material was
supplied to pipes other than the central pipe 11 of the burner, and
a hot wire anemometer was used to measure the variation of linear
velocity at the burner tip at a normal temperature. The gas was
N.sub.2 supplied as a sealing gas to the second pipe 12 at 4 L/min,
H.sub.2 supplied as a combustion gas to the third pipe 13 at 170
L/min, N.sub.2 supplied as a sealing gas to the fourth pipe 14 at 5
L/min, and O.sub.2 supplied as an auxiliary combustion gas to the
fifth pipe 15 at 40 L/min.
[0049] As shown in FIG. 4, the linear velocity was measured when
the gas inlet pipe 19 was oriented at four positions: a 0 o'clock
direction, a 3 o'clock direction, a 6 o'clock direction, and a 9
o'clock direction, which each differ by 90 degrees. For each
direction shown in FIG. 5, the upper side and the lower side (the
outer side and the inner side in the radial direction) of the
small-diameter gas discharge port nozzles were measured for the gas
discharge port 13P of the third pipe 13 containing the
small-diameter gas discharge port nozzles 16. The results are shown
in FIG. 6.
[0050] From FIG. 6 it is understood that, for each gas discharge
port, the gas linear velocity on the gas inlet pipe 19 side (0
o'clock direction) is high and the gas linear velocity on the other
side of the inner pipe (6 o'clock direction) is low.
First Embodiment
[0051] FIG. 7 is used to describe a burner 100 having a structure
of five coaxial pipes according to an embodiment of the present
invention. In this burner 100, eight small-diameter gas discharge
port nozzles 106N are contained in a third pipe 103, the
small-diameter gas discharge port nozzles 106N are arranged to
branch from the main pipe 108 at a position that is L=80 mm from
the burner 100 tip as shown in FIG. 7, the aperture diameter of the
third pipe 103 is 40 mm, and L/D=2.0.
[0052] The first pipe 101 and second pipe 102, which are farther
inward than the small-diameter gas discharge port 106P, have inner
diameters that begin contracting to be 83% of their original size
at a certain distance, i.e. a length Lx=120 mm, from the burner 100
tip, and the third to fifth pipes farther outside from the
small-diameter gas discharge port 106P have inner diameters that
begin decreasing to be 83% of their original size at a certain
distance, i.e. a length Ly=40 mm, from the burner 100 tip. The flow
rate and type of the gas supplied to each of the gas discharge
ports 101P to 106P was the same as in the preliminary
investigation, and the linear velocity variation was measured at a
normal temperature.
[0053] The results are shown in FIG. 8, and in comparison to the
preliminary investigation shown in FIG. 6, show a more uniform
linear velocity variation for each gas discharge port. As shown by
the thick arrows in FIG. 9, the gas flowing in the third pipe 103
was confirmed to have sufficiently moved around the back side of
the small-diameter gas discharge port nozzles 106N until reaching
the burner 100 tip.
[0054] Next, the inner diameters of the pipes on the source side of
the burner 100 for which the linear velocity variation measurement
was performed were changed, without changing the inner diameters of
the pipes on the tip side of the burner 100 or the position where
the inner diameters begin to contract. As a result, the contraction
ratio X (B/A) of the inner diameters of the pipes was changed in a
range from 0.7 to 1.0, glass fine particle deposition was
performed, and the deposition efficiency was calculated.
[0055] In the burner 100, the first pipe 101 was supplied with
SiCl.sub.4 as the glass raw material at 10 L/min and O.sub.2 as an
auxiliary combustion gas at 20 L/min, the second pipe 102 was
supplied with N.sub.2 as a sealing gas at 4 L/min, the third pipe
103 was supplied with H.sub.2 as a combustible gas at 170 L/min,
the fourth pipe 104 was supplied with N.sub.2 as a sealing gas at 5
L/min, the fifth pipe 105 was supplied with O.sub.2 as an auxiliary
combustion gas at 40 L/min, and the main pipe 108 of the
small-diameter gas discharge port nozzles 106N was supplied with
O.sub.2 as an auxiliary combustion gas at 16 L/min. Using these
gases, 100 kg of glass fine particles were deposited on a starting
member that was formed by fusing dummy rods with outer diameters of
50 mm to the ends of a core rod that has a length of 2000 mm and an
outer diameter of 50 mm.
[0056] As shown in FIG. 10, the results indicate that when the
contraction ratio is 0.83 or less, the linear velocity of the gas
becomes uniform, the flame is stabilized, and the deposition
efficiency becomes highly stable.
Comparative Example 1
[0057] The burner 100 for which linear velocity was measured in the
First Embodiment having an L/D ratio of 2.0 and a burner 100'
having the same source diameter, tip diameter, and contraction
position but having an L/D ratio of 1.5 as a result of setting the
length L of the small-diameter gas discharge port nozzles 106N to
be 60 mm were prepared. The flow rate and type of the gas provided
to each gas discharge port was the same as in the preliminary
investigation, and the linear velocity variation was measured for
each burner at a normal temperature.
[0058] As a result, upon comparing the burner 100' in which L/D=1.5
to the burner 100 in which L/D=2.0 and whose linear velocity
variation measurement results are shown in FIG. 8, it was found
that the burner 100' had a larger linear velocity difference
between the region inside the third pipe 103 and the region outside
the third pipe 103, i.e. above and below the small-diameter gas
discharge ports, as shown in FIGS. 11 and 12. This is assumed to be
because, since the length L of the small-diameter gas discharge
port nozzles 106N is insufficient relative to the aperture diameter
D of the gas discharge port 103P containing the small-diameter gas
discharge port nozzles 106N, the gas reaches the tip of the burner
100 without passing around inside the small-diameter gas discharge
port nozzles 106N.
Second Embodiment
[0059] The length L of the small-diameter gas discharge port
nozzles 106N of the burner 100' with L/D=1.5 used in Comparative
Example 1 was changed while keeping the same burner source
diameter, burner tip diameter, and contraction position to obtain a
burner 100'' having a different L/D ratio between the length L of
the small-diameter gas discharge port nozzles 106N and the aperture
diameter D of the third pipe 103. Next, 100 kg of glass fine
particles were deposited on a starting member that was formed by
fusing dummy rods with outer diameters of 50 mm to the ends of a
core rod that has a length of 2000 mm and an outer diameter of 50
mm. FIG. 13 shows the relationship between L/D and the deposition
efficiency.
[0060] In the burner 100'', the first pipe 101 was supplied with
SiCl.sub.4 as the glass raw material at 10 L/min and O.sub.2 as an
auxiliary combustion gas at 20 L/min, the second pipe 102 was
supplied with N.sub.2 as a sealing gas at 4 L/min, the third pipe
103 was supplied with H.sub.2 as a combustible gas at 170 L/min,
the fourth pipe 104 was supplied with N.sub.2 as a sealing gas at 5
L/min, the fifth pipe 105 was supplied with O.sub.2 as an auxiliary
combustion gas at 40 L/min, and the main pipe 108 of the
small-diameter gas discharge port nozzles 106N was supplied with
O.sub.2 as an auxiliary combustion gas at 16 L/min.
[0061] The results as shown in FIG. 13 indicate that, if the
expression L/D.gtoreq.2.0 is satisfied, a stable deposition
efficiency can be achieved since the small-diameter gas discharge
port nozzles 106N have sufficient length.
[0062] The above embodiments of the present invention achieve
advantageous effects such as the gas flow emitted from the burner
having a uniform linear velocity at the gas discharge ports, a
stable flame, and improved deposition efficiency of the generated
glass fine particles.
[0063] Usually, the gas introduced to the gas discharge ports from
the gas inlet pipes has a linear velocity variation within the
annular flow path. The gas introduced from a direction orthogonal
to the axis of the gas discharge ports changes direction after
colliding with a wall of an inner pipe within the burner and moves
toward the tip of the burner, and so it is difficult for this gas
to pass around the opposite side, i.e. the back, of the inner pipe.
As a result, the linear velocity is larger on the gas inlet pipe
side and smaller on the back sides of the inner pipes. However, by
adopting the configuration of the above embodiments in which the
inner diameters of the pipes contract until reaching the gas
discharge ports, even when there are inner pipes, the gas flow
within the annular flow path collides with an inner wall that is
slanted relative to the axial direction and disperses. Therefore,
by making it easier for the introduced gas to reach the backs of
the inner pipes, the linear velocity variation in the annular flow
path can be restricted.
[0064] Concerning the gas discharge ports positioned farther
outward than the gas discharge port that contain the small-diameter
gas discharge port nozzles, by contracting the flow path in the
same location as the gas discharge port containing the
small-diameter gas discharge port nozzles, the linear velocity can
be made uniform within the gas discharge ports, without increasing
the size of the burner. On the other hand, by contracting the inner
diameters of pipes forming the gas discharge ports positioned
farther inward than the small-diameter gas discharge port nozzles
at a portion of the main pipe before it branches into the
small-diameter gas discharge port nozzles, i.e. a position farther
on the burner source side than the branching point, the gas flow
can be dispersed in the flow path, the linear velocity variation
can be restricted, and the diameters of the inner pipes passing
through the branching portion can be decreased. As a result, the
space between the branched small-diameter gas discharge port
nozzles can be filled to make the overall burner more compact.
[0065] If the pipes forming the gas discharge ports positioned
farther inward than the small-diameter gas discharge port nozzles
contract at a position farther on the burner tip side than the
branching point, the gas flow in the contracted portion is diffused
and the linear velocity variation is restricted, but since the
diameter of the inner pipes is still large the space between the
small-diameter gas discharge port nozzles after branching cannot be
filled, and so this space must be increased. As a result, the gas
discharge port containing the small-diameter gas discharge port
nozzles and the pipes farther outward are thicker, which causes the
burner to be undesirably large.
[0066] By setting the small-diameter gas discharge ports in the
same row in the small-diameter gas discharge port nozzles to have
the same focal distances, the gas emitted from the gas discharge
ports can be focused on a single target point, thereby increasing
the reactivity of the gas. Accordingly, the deposition efficiency
of the porous glass can be improved.
[0067] Here, the contraction ratio of the inner diameters of the
pipes forming the gas discharge ports is important, and with the
inner diameters of the pipes on the burner source side represented
as A and the inner diameters of the pipes on the burner tip side
represented as B, setting this contraction ratio X such that
X=B/A.ltoreq.0.83 causes the gas used for manufacturing the porous
glass base material to have a more uniform linear velocity. A
higher flow rate for the gas introduced to the annular flow path
tends to result in less linear velocity variation, and so the
contraction ratio X should be larger for higher flow rates. When
the pipes forming the gas discharge ports are cylindrical, the
diameter thereof in a cross section in the axial direction is
uniform, and so the contraction ratio X for each pipe is a ratio
between the diameter A of the pipe on the burner source side and
the diameter B of the pipe on the burner tip side. If the pipes
forming the gas discharge ports have cross sections that are
ellipses or polygons, the diameter of the cross section in the
axial direction differs depending on the position around the
center. In this case, the contraction ratio X can be a value
obtained by comparing the diameter of the pipe at any location
around the center on the burner source side (A) to the identically
measured diameter on the burner tip side (B).
[0068] Depending on the type and flow rate of the inducted gas, if
the length L of the small-diameter gas discharge port nozzles is
short even though the inner diameter of the pipe is contracted, the
gas flowing around the small-diameter gas discharge port nozzles
has different linear velocity in the inner pipes than in the outer
pipes of the flow path, causing a linear velocity variation (FIG.
11). This variation is due to the length L of the small-diameter
gas discharge port nozzles being too small with respect to the
aperture diameter of the gas discharge port containing the
small-diameter gas discharge port nozzles.
[0069] If the length L of the small-diameter gas discharge port
nozzles is sufficient with respect to the aperture diameter of the
gas discharge port containing the small-diameter gas discharge port
nozzles, the gas moves inward in the radial direction of the
small-diameter gas discharge port nozzles until reaching the burner
tip, and this decreases the difference in linear velocity around
the small-diameter gas discharge port nozzles (FIG. 9). On the
other hand, if the length L of the small-diameter gas discharge
port nozzles is insufficient with respect to the aperture diameter
of the gas discharge port containing the small-diameter gas
discharge port nozzles as described above, the gas does not move
inward in the radial direction of the small-diameter gas discharge
port nozzles until reaching the burner tip. As a result, the linear
velocity inside the small-diameter gas discharge port nozzles is
decreased, causing a large difference in the overall linear
velocity.
[0070] With the aperture diameter of the gas discharge port
containing the small-diameter gas discharge port nozzles
represented as D, sufficient length L for the small-diameter gas
discharge port nozzles can be achieved by setting the length L from
the branching point to the burner tip such that L/D.gtoreq.2.0, and
this causes the linear velocity of the gas flowing around the
small-diameter gas discharge port nozzles to be uniform.
[0071] The burner source side must be sturdy since the burner is
fixed to a holding device, and the burner tip side must have pipes
with contracting inner diameters. Therefore, the pipes positioned
farther inward than the gas discharge port containing the
small-diameter gas discharge port nozzles preferably become thinner
from the portion where the inner diameter begins to contract to the
burner tip.
[0072] The burner tip side of the outermost pipe of the burner is
tapered due to the contraction of the inner diameters of the pipes.
Therefore, the burner cover also contracts to maintain a prescribed
clearance with respect to the outermost pipe of the burner.
[0073] While the embodiments of the present invention have been
described, the technical scope of the invention is not limited to
the above described embodiments. It is apparent to persons skilled
in the art that various alterations and improvements can be added
to the above-described embodiments. It is also apparent from the
scope of the claims that the embodiments added with such
alterations or improvements can be included in the technical scope
of the invention.
[0074] The operations, procedures, steps, and stages of each
process performed by an apparatus, system, program, and method
shown in the claims, embodiments, or diagrams can be performed in
any order as long as the order is not indicated by "prior to,"
"before," or the like and as long as the output from a previous
process is not used in a later process. Even if the process flow is
described using phrases such as "first" or "next" in the claims,
embodiments, or diagrams, it does not necessarily mean that the
process must be performed in this order.
[0075] As made clear from the above, the embodiments of the present
invention can be used to realize a burner that achieves a stable
flame, improves the glass fine particle deposition efficiency, and
significantly improves the ability to produce porous glass base
material.
* * * * *